The invention presented here involves a device and a process for the quantified assessment of the physiological impression of reflective surfaces and particularly of painted surfaces.
For numerous technical products, the quality of the visible surfaces is a critical characteristic for the overall impression of the product. The technical problems which thereby arise are hereafter clarified using the construction of surfaces of motor vehicle bodies which by no means, however, should be understood as a restriction for the application of the invention presented here.
Motor vehicles are usually given a high-gloss paint whose gloss value as a rule far exceeds the gloss value of other surfaces, e.g., furniture surfaces and the like. The high gloss of the paint used and the relatively large surfaces require an exceptionally careful preparation of the areas being painted and a very careful application of the paint. In order to recognize deficiencies in the quality of painted body surfaces, automobile manufacturers today engage a large number of testers who visually test the quality of the surfaces. However, this method involves several disadvantages.
The job of the testers is very demanding and requires work areas whose light conditions are always exactly defined. However, large differences in the evaluation of the same painted surfaces by different testers have been observed, since on the one hand the respective physiological impression is different from tester to tester and since on the other hand the visual faculty of the individual tester is also dependent on his respective physical condition. There are thus great difficulties in defining a lower quality limit which can no longer be accepted without deficiencies and which requires a new painting of the vehicle body. In addition, it is also difficult on the part of experienced testers to determine the causes for unevenness in the paint, so that it is difficult to change the control values of an automatic painting device for improving the quality, based on the observations thus made.
DE-OS 2,946,493 describes a process for assessing the evenness of optically reflecting surfaces. In this process, the surface being tested is illuminated with a point source of light (in the example a 100 Watt halogen lamp and a perforated screen) at a defined distance (in the example 1 m). The light beam which is reflected by the surface being tested is rendered visible on a focusing screen, whereby the brightness distribution of the reflected light depends on the surface structure. In order to determine the brightness distribution, the surface being tested is moved with respect to the lamp and the reflected light is recorded by means of a stationary photodetector. In the example, this photodetector is set up 25 cm from the surface being tested. The variations in brightness then serve as a measurement for evaluating the quality of the surface. The detailed presentation in DE-OS 2,946,493 is referred to concerning the additional state of the art.
The process described above has not been feasible in practice. The reason can be seen primarily in the fact that although a quality index is determined for the quality of the surface, this quality index is not sufficient for characterizing the physiological impression applicable to the evaluation of the surface being tested.
The problem of the invention presented here is, therefore, to further develop a process and a device of the type mentioned above that yields a reproducible, quantified assessment of the physiological impression of reflective surfaces.
An additional aspect of the problem is to create a device which is small and easily constructed and which is designed in such a manner that it can be used by one operator without additional auxiliary devices for the quantified assessment of a surface.